Dr. Agnew is currently working to develop more quantitative connections between the microstructure and properties (primarily mechanical) of advanced crystalline materials through experimentation and modeling.

The properties of most crystalline materials exhibit anisotropies characteristic of their crystal symmetry and "orientation related effects" ultimately impact materials performance in every modern industry.

As an example, elastic deformation behavior is affected by the presence of textures or other complex microstructures and we have a project which focuses on the interaction between elastic (ultrasonic) waves and microstructure. Presently, these interactions are viewed as deleterious for the nondestructive evaluation (NDE) of components (e.g. weldments or forgings.) We are investigating the possibility that quantitative assessments of the microstructure might be made in a nondestructive fashion.

Plastic deformation is particularly interesting in the context of textures since it is often responsible for the observed textures in the first place, and because it is subsequently affected by the presence of texture. Polycrystal plasticity modeling has been successfully employed to predict texture evolution and resultant anisotropy. Further, these models may be used to solve the inverse problem of identifying deformation mechanisms involving dislocation slip and/or mechanical twinning. Finally, thin films and coatings often exhibit strong textures due to preferred growth kinetics, or high internal/residual stresses.

Experimentally, we use a variety of diffraction-based tools to measure the orientation and stress-state of invdividual grains and polycrystals ranging from electron diffraction in an SEM (EBSD) or TEM, to x-ray diffraction in our home laboratory or at a synchrotron, to neutron diffraction at a reactor or pulsed neutron source. These structural measurements are linked to measurements of the mechanical properties measured using universal testing machines, formability tests, or ultrasonic testing. A favorite approach is to link mechanical behavior and characterization techniques through the use of in-situ testing where the material is characterized during deformation.

Education

Ph.D. Northwestern University, 1998; B.S. Cornell University, 1994

By this Researcher

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